1. Field
The present invention relates to a semiconductor light emitting device and its manufacture method, and more particularly to a nitride semiconductor light emitting device and its manufacture method.
2. Related Art
External emission efficiency of a nitride semiconductor light emitting device is desired to be further improved. Description will be made by using a typical nitride semiconductor light emitting device as an example. On a transparent substrate such as sapphire, a GaN buffer layer grown at a low temperature, an n-type GaN layer, an emission layer and a p-type GaN layer are grown and laminated in this order by metal organic chemical vapor deposition (MOCVD) or the like. Band gap of GaInN formed by replacing a portion of Ga of GaN with In becomes narrower than that of GaN, whereas band gap of GaAlN formed by replacing a portion of Ga of GaN with Al becomes broader than that of GaN. AlN may be epitaxially grown on GaN. AlxInyGaN (0≦x≦1, 0≦y≦1, 0<z≦1, x+y+z=1) is called nitride semiconductor. It is possible to adjust the characteristics of a semiconductor light emitting device, by selecting compositions of AlGaInN.
Emission in an emission layer is omnidirectional. Light propagating toward a flat surface and reaching at an incidence angle of a critical angle or larger is totally reflected at the surface. It is not easy to externally emit light once totally reflected at the surface. It is known that if texture (irregularity) is formed on the surface, it becomes possible to improve an external emission efficiency.
Japanese Patent Publication No. 3469484 proposes a method of processing the surface of a p-type nitride semiconductor layer by dry etching or ion milling to form texture (irregularity).
There is a possibility that dry etching or ion milling may damage a processed layer and increase contact resistance. Development is being made to further improve external emission efficiency.